How do I know if my solar trickle charger is working?
I attached a solar trickle charger to a small lead-acid battery. I tested the panel alone and it was producing 19v, but when I attached it to the battery the voltage was the same as the battery alone (12.44v). I then put a multimeter between the positive output of the panel and the positive on the battery to see if any current was flowing into the battery, and it said 0mA, so I would assume that it is not working. Is the panel just not big enough for the battery or am I missing something?
19V is good for charging a 12V battery, once connected to the battery it will get pulled down to the battery voltage. If the battery is measuring 12.44V it sounds like it is really low, it should be close to 14V when full. Depending on the size of the solar panel, it will likely take days to charge it back up.
You can test the solar panel without the battery with the amp meter. Just set the meter to measure amps, you may need to move one of the leads, and measure across the plus and minus wires like you did to measure the voltage. You can watch this video for step by step instructions http://www.altestore.com/video/video-Solar-Panel-Testing-v3/. If there is current, it is working. If the battery doesn’t get charged after a few days, the battery may be dead from being drained too much.
I suppose that you could put a potentiometer across the solar panel leads and increase the resistance till the voltage across the solar panel is 19V again then you could calculate the current by measuring the resistance in case the solar panel simply doesn’t have the wattage to do anything measurable. That should give you an idea as to whether the solar panel is giving you the rated power. There’s no doubt that a lead acid battery would overwhelm a small solar panel hence the "trickle charger" label. The only true test is if the voltage across the battery manages to increase over time.
If you connect a diode between the panel and the battery, will the voltage across the panel leads read 0.6 volts higher then the voltage across the battery leads? That would mean some current is flowing for the diode to let it through. It would be a good idea to have such a diode to limit self discharge through the panel anyways.
19V open circuit is the right voltage, and it’s normal for that to drop to about 12 when charging the battery.
I’m surprised that the current reads 0 – that does not seem right at all. Check your multimeter – is there a different place that you plug the test lead in to measure current? Also, try measuring the current by (briefly) connecting the multimeter across a AA battery (NOT the lead acid battery, that’s too powerful), just to make sure your meter is good.
Even a really junky panel should deliver at least a few mA. Did you try measuring the current of the panel alone (that is, the short circuit current)? If the panel can produce 19V open circuit, surely it has some measurable short circuit current.